Dalian Chemical Institute proposed a new way of large-scale resource coupling utilization of carbon dioxide

In today’s world, green and low-carbon development is the trend of the times, and the whole world is constantly working towards the goal of carbon neutrality. The emission reduction of carbon dioxide (CO2) is inseparable from the realization of the “dual carbon” goal, and the large-scale and high value-added utilization of CO2 as a carbon resource is an important strategic direction that is extremely challenging. Recently, the team of academician Liu Zhongmin of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences proposed a new way to prepare aromatic bulk chemicals by coupling CO2 and alkanes. The team found that the use of acid zeolite as a catalyst can catalyze the coupling reaction between CO2 and light alkanes, while promoting the formation of aromatic hydrocarbons, and the selectivity of aromatics in the product is as high as 80%. Under specific conditions, about 3/4 of CO2 is converted into carbon monoxide products that can be used as chemical raw materials, and further studies confirm that about 1/4 of the carbon atoms of converted CO2 directly enter the aromatic products. The relevant results were published in the Chinese catalysis professional journal “Chinese Journal of Catalysis”.

Photo courtesy of Dalian Chemical Properties

CO2 is the most stable chemical molecule, and efficiently converting CO2 as a feedstock into bulk chemicals has always been a challenge. Aromatics are important basic raw materials in organic chemicals, which can be widely used in synthetic resins, fibers, dyes, medicines, fragrances, etc., and are currently mainly produced by petrochemical routes such as naphtha catalytic reforming, and there is a problem of hydrocarbon imbalance between raw materials and target products. The introduction of CO2 and hydrogen-rich alkanes to couple to regulate the hydrocarbon balance of their reactions, improve the selectivity of target products, and convert CO2 into useful chemical raw materials or products to realize CO2 resource utilization, which is of transformative significance to traditional aromatic production technology. Many researchers have previously tried to use CO2 to react with alkanes to convert CO2 into CO and reduce the production of hydrogen, but they believe that the carbon atoms of CO2 do not enter the hydrocarbon products.

Using HZSM-5 zeolite as catalyst, the coupling reaction between CO2 and light alkanes was catalyzed to generate aromatics

In this work, the team used HZSM-5 molecular sieve as a catalyst to compare and study the conversion reactions of n-butane, n-pentane and n-hexane in helium and CO2 atmospheres, and studied in detail the effects of molecular sieve acidity, reaction temperature, pressure, CO2 addition and other conditions on the coupling reaction. The results showed that the introduction of CO2 could greatly promote the formation of aromatic hydrocarbons, while the formation of small alkanes such as methane and ethane was inhibited.

Analysis of the catalyst after the reaction revealed a large number of oxygen-containing species such as methyl-substituted lactone and methyl-substituted cyclic enone. Through isotope labeling experiments and a series of verification experiments, it was confirmed that these oxygen-containing intermediates were generated by the coupling conversion of CO2 and hydrocarbons, and the pathway of coupling reaction was proposed and proved, that is, CO2 reacted with carboc-cations to obtain cyclolactone, cyclolactone was further converted to methylcycloenone, and methylcycloenone was converted to aromatic hydrocarbon products. Furthermore, density functional theory is used to calculate the energy barrier of each step of the coupling reaction mechanism, and the feasibility of the coupling reaction mechanism is verified.

“The biggest highlight of this achievement is that it is confirmed that the coupling reaction between CO2 and alkanes can not only convert it into carbon monoxide, but more importantly, the carbon atoms of some CO2 can directly enter the aromatic products, promote the formation of aromatic hydrocarbons and improve the selectivity of aromatic hydrocarbons in the products, which provides an effective way for the large-scale resource utilization of CO2 and has broad application prospects.” Liu Zhongmin introduced.

The research results were published in the only English journal of catalysis indexed by SCI in China – Journal of Catalysis. Publishing excellent results in domestic journals, Academician Liu Zhongmin has a deep understanding. “The use of CO2 as a carbon resource for high value-added utilization is of great significance to the design of the technical path to achieve the dual carbon goal. Publishing our latest research progress in domestic journals is carefully considered. To strengthen scientific and technological innovation in China, it also needs international journals that are compatible with the status of scientific and technological innovation. In recent years, many domestic journals have opened up a green channel for high-level research work, and articles will be quickly published and promoted after acceptance, and the degree of display at home and abroad has gradually improved. Liu Zhongmin told China Science News, “Domestic journals represented by the Journal of Catalysis have been rapidly improving their professionalism and world influence in recent years, allowing China’s latest achievements to be published in Chinese journals, which also reflects the continuous enhancement of our scientific and technological confidence.” At the same time, the development of first-class journals is also inseparable from first-class scientific research results, actively submit high-level scientific research results to domestic journals, need everyone’s active support, first of all, start from yourself, we and domestic journals are ‘win-win’. (Source: Sun Danning, China Science News)

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